The study of identical (monozygotic) and fraternal (dizygotic) twins provides a unique opportunity to investigate the role of genetic and environmental factors in ocular diseases. If concordance (agreement) rates for monozygotic (MZ) twins is much higher than for dizygotic (DZ) twins, one may assume a genetic mechanism is involved in the disease. The National Academy of Sciences-National Research Council (NAS-NRC) maintains a registry of almost 16,000 adult make MZ and DZ twins who are veterans of WW II. There are 250 twin pairs (500 twins) with both members alive and living in or around Chicago, Illinois. A sample of 60 twin pairs (30 MZ and 30 DZ) will be chosen for a pilot study of the epidemiology and heritability of age-related macular drusen, refractive errors and lens changes. Macular drusen are a precursor of age-related macular degeneration, the leading cause of adult blindness in the United States. Cataracts are the third leading cause of adult blindness in the U.S. A better understanding of genetic and environmental influences on these diseases will hopefully lead to earlier diagnosis, improved treatment, and the prevention of blindness in a large segment of the population. It may also provide information about high risk populations. This pilot study will be used as the basis for requesting funding to do a cross-sectional study of a much larger population of twins. Following the prevalence survey, we plan to do a longitudinal study investigating the incidence and rate of progression of drusen, and the development of macular degeneration.